The objective of this research is to employ genetic and biochemical techniques to elucidate the previously described but poorly understood relationships between purine and pyrimidine metabolism and DNA repair, mutagenesis, and carcinogenesis in mammalian cells. An established line of S49 T-lymphoma cells from which we have isolated mutant lines which have alterations in enzymes involved in purine or pyrimidine metabolism will be used to determine the importance of these various enzymes in providing DNA precursor deoxyribonucleotides for the repair of DNA following treatments which damage DNA. Since the enzymes ribonucleotide reductase and thymidylate synthetase are central to the de novo synthesis of deoxyribonucleotides, I want to isolate and study cell lines with mutations in these enzymes to determine how these mutations affect DNA repair and mutagenesis. In addition, I want to determine whether imbalances in purine or pyrimidine deoxyribonucleotide levels play a role in the induction of specific mutagenic DNA repair pathways in mammalian cells. Finally, I want to isolate a series of mutant cell lines which are either more sensitive, or more resistant to UV-irradiation, or to other chemical agents which damage DNA such as bleomycin or mitomycin C. These mutants will be characterized with respect to their deoxyribonucleotide metabolism and their susceptibility to induced mutagenesis.